Several types of passenger conveyor systems, such as, escalators, moving walkways, moving sidewalks, etc. are widely used these days to effectively transport pedestrian traffic (or other objects) from one location to another. Areas of usage of these passenger conveyor systems often include airports, hotels, shopping malls, museums, railway stations and other public buildings. Such passenger conveyor systems typically have two landings (e.g., a top landing and a bottom landing) that bridge a truss structure. Moving handrails, as well as a plurality of steps/treads guided by a step chain (also called an escalator chain) in a loop transport the pedestrian traffic between the two landings. The step chain can be guided (e.g., driven) by a step chain sprocket. In particular, the passenger conveyor systems generally include a drive module having a motor and a main shaft, which drives one or more main drive chain sprockets, which in turn drives the step chain sprocket for moving the plurality of steps in the endless loop.
The interaction of the step chain with the step chain sprocket often produces fluctuations and vibrations. By way of background, a step chain includes a plurality of discrete step chain links connected together by way of connecting links, such as, a pin and a link plate or a roller, while a sprocket (e.g., the step chain sprocket) includes a profiled wheel having a plurality of engaging teeth for meshing and engaging the connecting links (or possibly even engaging the step chain links) of the step chain for moving the step chain as the step chain sprocket rotates. The engagement of the connecting links of the step chain with the engaging teeth of the step chain sprocket causes the step chain to vibrate and fluctuate. These vibrations and fluctuations are often called a polygon effect or a chordal action and not only affect the ride experience of a user (who typically feels these vibrations and fluctuations aboard the passenger conveyor system), but it also causes undesirable friction between the step chain and the step chain sprocket, thereby reducing the lifespan of those components. Noise generated by the vibrations resulting from the engagement of the step chain with the step chain sprocket is another concern.
Therefore, mitigating or compensating the polygon effect is desirable. Several solutions to reduce or otherwise mitigate the polygon effect have been proposed in the past. Generally speaking, the intensity of polygon effect depends upon the velocity (frequency) of the step chain and the amplitude of the step chain pitch−step chain sprocket pitch. The greater the step chain pitch, the higher the polygon effect. To reduce the polygon effect, therefore, the pitch of the step chain can be reduced. Thus, one approach of mitigating the polygon effect involves increasing the number of step chain links in the step chain (which can reduce the step chain pitch), and/or correspondingly increasing the diameter of the step chain sprocket(s) to increase the number of teeth thereon (which may also effectively reduce the step chain pitch). This technique, although effective in improving the riding experience of a user, nonetheless has several disadvantages.
For example, due to the increase in the number of the parts (e.g., increase in the number of step chain links and other associated parts, such as, rollers, pins, bushings, link plates, etc., of the step chain, and/or a bigger sprocket), the overall cost of the associated system increases. Furthermore, the maintenance involved with the upkeep of the increased number of components goes up as well, and so does the amount of lubricant needed to reduce the increased wear and tear amongst those components. This increased wear and tear can additionally reduce the lifespan of the step chain and the step chain sprocket. Moreover, the aforementioned approach does not address the noise issue discussed above, and may in fact increase the noise due to a greater engagement of the step chain with the step chain sprocket.
Accordingly, there is a need for an effective solution to compensate the polygon effect that does not suffer from the disadvantages mentioned above. Particularly, it would be beneficial if a polygon compensation technique were to be developed that improved the riding experience of the users without incurring any additional costs associated with increasing the step chain links or using a bigger step chain sprocket. It would further be beneficial if such a technique were reliable, easy to maintain, increased (or at least did not negatively impact) the lifespan of the step chain and the step chain sprocket (e.g., by reducing wear and tear), and additionally provided a greener approach (by using less lubricant) to solving the polygon effect problem. It would additionally be desirable if this technique reduced the noise generated by the step chain and the step chain sprocket engagement.